Title: Equation of state for two flavor QCD at N{sub t}=6

Abstract

We calculate the two flavor equation of state for QCD on lattices with lattice spacing a=(6T){sup {minus}1} and find that cutoff effects are substantially reduced compared to an earlier study using a=(4T){sup {minus}1}. However, it is likely that significant cutoff effects remain. We fit the lattice data to expected forms of the free energy density for a second order phase transition at zero-quark mass, which allows us to extrapolate the equation of state to m{sub q}=0 and to extract the speed of sound. We find that the equation of state depends weakly on the quark mass for small quark mass. {copyright} {ital 1997} {ital The American Physical Society}

@article{osti_656096,
title = {Equation of state for two flavor QCD at N{sub t}=6},
author = {Bernard, C. and Blum, T. and DeTar, C. and Gottlieb, S. and Rummukainen, K. and Heller, U.M. and Hetrick, J.E. and Toussaint, D. and Kaerkkaeinen, L. and Sugar, R.L. and Wingate, M.},
abstractNote = {We calculate the two flavor equation of state for QCD on lattices with lattice spacing a=(6T){sup {minus}1} and find that cutoff effects are substantially reduced compared to an earlier study using a=(4T){sup {minus}1}. However, it is likely that significant cutoff effects remain. We fit the lattice data to expected forms of the free energy density for a second order phase transition at zero-quark mass, which allows us to extrapolate the equation of state to m{sub q}=0 and to extract the speed of sound. We find that the equation of state depends weakly on the quark mass for small quark mass. {copyright} {ital 1997} {ital The American Physical Society}},
doi = {10.1103/PhysRevD.55.6861},
journal = {Physical Review, D},
number = 11,
volume = 55,
place = {United States},
year = 1997,
month = 6
}

Using Taylor expansions of the pressure obtained previously in studies of 2-flavor QCD at nonzero chemical potential we calculate expansion coefficients for the energy and entropy densities up to O({mu}{sub q}{sup 6}) in the quark chemical potential. We use these series in {mu}{sub q}/T to determine lines of constant entropy per baryon number (S/N{sub B}) that characterize the expansion of dense matter created in heavy ion collisions. In the high temperature regime these lines are found to be well approximated by lines of constant {mu}{sub q}/T. In the low temperature phase, however, the quark chemical potential is found to increasemore » with decreasing temperature. This is in accordance with resonance gas model calculations. Along the lines of constant S/N{sub B} we calculate the energy density and pressure. Within the accuracy of our present analysis we find that the ratio p/{epsilon} for T>T{sub 0} as well as the softest point of the equation of state (p/{epsilon}){sub min}{approx_equal}0.075, show no significant dependence on S/N{sub B}.« less

A first study of critical behavior in the vicinity of the chiral phase transition of (2+1)-flavor QCD is presented. We analyze the quark mass and volume dependence of the chiral condensate and chiral susceptibilities in QCD with two degenerate light quark masses and a strange quark. The strange quark mass (m{sub s}) is chosen close to its physical value; the two degenerate light quark masses (m{sub l}) are varied in a wide range 1/80{<=}m{sub l}/m{sub s}{<=}2/5, where the smallest light quark mass value corresponds to a pseudoscalar Goldstone mass of about 75 MeV. All calculations are performed with staggered fermionsmore » on lattices with temporal extent N{sub {tau}}=4. We show that numerical results are consistent with O(N) scaling in the chiral limit. We find that in the region of physical light quark mass values, m{sub l}/m{sub s}{approx_equal}1/20, the temperature and quark mass dependence of the chiral condensate is already dominated by universal properties of QCD that are encoded in the scaling function for the chiral order parameter, the magnetic equation of state. We also provide evidence for the influence of thermal fluctuations of Goldstone modes on the chiral condensate at finite temperature. At temperatures below, but close to the chiral phase transition at vanishing quark mass, this leads to a characteristic dependence of the light quark chiral condensate on the square root of the light quark mass.« less